An in-vehicle radar may receive not only reflected waves of radar waves transmitted from the in-vehicle radar of an own vehicle but also radar waves transmitted from an in-vehicle radar of another vehicle, such as an oncoming vehicle and a parallel running vehicle, present in the vicinity of the own vehicle. Thereby, so-called interference between the in-vehicle radars may occur.
When an FMCW is used as a radar wave, if interference occurs with an FMCW or a multifrequency CW transmitted from another apparatus, a waveform of a beat signal is formed by superimposing a waveform having a signal component having a high frequency due to interference on a waveform of a beat signal to be detected (refer to FIG. 5(a)).
Focusing on this point, techniques are known in which points are extracted where signal levels of a beat signal become maximum or minimum, and if the extracted points do not appear at periodical timings, it is determined that interference with another in-vehicle radar apparatus has occurred (for example, refer to Patent Literature 1).